Physics
Scientific paper
Jun 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51.1665f&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 51, Issue 6, pp.1665-1673
Physics
9
Scientific paper
An extraction-quench apparatus was used to measure calcite solubilities in supercritical CO 2 ---H 2 O mixtures. Experiments were conducted at 1 kbar and 2 kbar, between 240°C and 620°C and from X CO 2 = .02 to X CO 2 = .15 in order to determine the solubility behavior as a function of pressure, temperature and CO 2 content. The results indicate that calcite solubilities under these conditions behave similarly to previously investigated calcite solubilities at lower pressures and temperatures (SHARP and Kennedy, 1965). At constant X CO 2 , the solubility increases with increasing pressure, but it decreases with increasing temperature. When the temperature and pressure are constant, the calcite solubility rises with increasing X CO 2 to a maximum value at X CO 2 between 0.02 and 0.05. For higher CO 2 contents, up to X CO 2 = .15, the calcite solubility decreases, probably due to the decrease of H 2 O activities to values significantly below unity. The solubility behavior can be successfully modeled by making the assumption that Ca ++ is the dominant calcium species and that the carbon-bearing species are CO 2(aq) and HCO - 3 . Since for these dilute H 2 O---CO 2 fluids, all activity coefficients can be assumed to not differ significantly from unity, ionization constants for the reaction H 2 O + CO 2(aq) H + + HCO - 3 can be calculated at 1 and 2 kbar between 250°C and 550°C. These calculated values are in good agreement with the low temperature determinations of the ionization constants for this reaction determined by Read (1975). Values of the molal Gibbs free energy of CO 2(aq) obtained in our study exhibit a much greater positive departure from ideality than those calculated with the modified Redlich-Kwong equations of either Flowers (1979) or Kerrick and Jacobs (1981) for dilute CO 2 aqueous solutions.
Fein Jeremy B.
Walther John V.
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